During maintenance activities, firearms such as rifles (or sub-components thereof) are often held or otherwise supported by clamps, jigs, or other mechanical support arrangements. This can free up an armorer's hands for performing maintenance tasks, and can provide more secure support than, for example, handholding. Vise blocks that facilitate support of a rifle with a bench vise via attachment to the rifle's ammunition magazine well (“magwell”) are known, but many such vise blocks suffer from an imprecise fit between block and magwell. It would be desirable to provide vise blocks that can provide secure support for a firearm via magwell attachment.